Preparation of submicron titanium nitride powder by vapor-phase reactions
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INTRODUCTION
T U N G S T E N carbide is extensively used for C-5 grade cutting tools, wear-resistant parts, and other applications, because the material exhibits high hardness, transverse rupture strength, and abrasion-resistant properties. It is usually bonded with a cobalt binder and titanium carbide and tantalum additives by compactions and sintering to form cemented carbide shapes. [lj Within the past two decades, the tool industries have developed technology for coating cemented carbides with multilayered titanium nitride (TIN), titanium carbide (TIC), and alumina (A1203) by physical and chemical vapor deposition techniques, t2-51 These coatings have increased the wear resistance of parts and extended the life of cutting tools by a factor of 5 or more. t61 However, the manufacturing of these coated tools is dependent on critical imported materials used in making the cemented carbide base material. The United States is almost wholly dependent upon imported tungsten, cobalt, and tantalum, because the nation lacks adequate deposits of these strategic and critical materials. To help reduce this dependency, the United States Bureau of Mines is conducting research to devise substitute materials for cutting tools and wear-resistant parts. To date, the Bureau has devised several different compositions of nickel-alloy bonded TiC.t71 Another potential tungsten carbide substitute is TiN, which the Japanese report forms a suitable cermet and exhibits properties comparable to those of cemented carbides, tS] Moreover, changing market requirements are stimulating the development of new engineering materials for manufacturing sintered parts that exhibit greater hardness and strength, higher strength-density ratios, and other superior properties when compared to traditional materials. [9-13] Efforts to utilize submicrometer nonoxide materials, such as silicon nitride (Si3N4) , titanium diboride (TiB2), and titanium nitride (TIN), in making reliable sintered parts have been only partially successful.
G.W. ELGER, Research Chemist (Retired), D.E. TRAUT, Supervisory Chemical Engineer, G.J. SLAVENS, Chemical Engineer, and S.J. GERDEMANN, Chemical Engineer, are with the Albany Research Center, Bureau of Mines, United States Department of the Interior, Albany, OR 97321-2198. Manuscript submitted August 31, 1987. METALLURGICAL TRANSACTIONS B
The lack of high-purity powders of uniform quality and narrow particle size range has been a major problem in making reliable parts. The nonoxide powders are made by several different techniques, including vapor-phase reactions, plasma technology, [",131 and the reaction of titanium hydride with ammonia (NH3) gas in the presence of a nickel catalyst at 800 ~ In 1985, the Bureau initiated an investigation that employed vapor-phase reactions to synthesize TiN, TiC, and Ti(C,N) powders. I151 For example, TiN was synthesized by reducing titanium tetrachloride (TIC14) with sodium (Na) or magnesium (Mg) in the presence of N 2 at 750 ~ to 1050 ~ The powder products were collected and leached in hy
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